The present invention relates in general to an electrode substrate for a fuel cell of phosphoric acid type, and more in detail, relates to an electrode substrate provided with peripheral sealers for a fuel cell, comprising
two porous and carbonaceous electrodes respectively provided with flow channels of the reactant gas, said electrodes being joined to the both surfaces of a separator via a flexible graphite sheet so that said flow channels in one of said electrodes are perpendicular to those in another said electrode and said separator having the extended part which extends beyond a periphery of said electrode which is parallel to said flow channels in said electrode and
each peripheral sealer on the side of said electrode parallel to said flow channels therein, which comprises a gas impermeable and compact carbon material, said peripheral sealer being joined to said extended part of said separator via a flexible graphite sheet,
the whole composite materials being formed into one body as carbon by calcination thereof under a reduced pressure and/or in an inert atmosphere, and a process for producing the electrode substrate.
In general, the substrates as the electrode in the fuel cell of a phosphoric acid type are stacked so that its one surface is contacted to the phosphoric acid matrix and its another surface is contacted to the separator. In addition, in order to make a fuel cell by stacking the electrode substrates, a seal material is disposed on the edge part thereof to prevent the leakage of the reactant gas from the side of the electrode substrate of the cell to outside.
In such a fuel cell, the joining between the composite materials of the fuel cell has hitherto been carried out by the use of carbon cement. Since carbon cement is erroded by phosphoric acid, there has been possibility of causing exfoliation of the composite materials and of leakage of the reactant gas through the joined parts.
Moreover, since the electrode substrate takes generally a thin-plate form, there has been a problem from the view point of mechanical strength, namely, the electrode substrate is broken in handling, particularly in the case where the surface area of the electrode substrate is large enough.
As a result of the present inventors' studies on the process for producing the electrode substrate for a fuel cell, which does not have the above-mentioned defects, it has been found by the present inventors that the electrode substrate provided with the peripheral sealers on the side of the electrode parallel to the flow channel therein, in which the separator, the electrode and the peripheral sealers have been joined together via flexible graphite sheet(s) and have been calcined into one body as carbon is particularly excellent in resistance to phosphoric acid and at the same time, since the peripheral sealers have been evenly disposed on and joined to the peripheral part of the substrate while holding the separator from both sides thereof in a crossed state and they are calcined to be one body as carbon, there is a reinforcing effect, and that the electrode substrate of the above-mentioned construction is excellent in handling property, and on the basis of their findings, the present inventors have attained the present invention.
The first object of the present invention is to provide an electrode substrate provided with peripheral sealers for a fuel cell, in which the peripheral sealers for the reactant gas have been joined to the separator and have been made into one body as carbon.
The second object of the present invention is to provide an electrode substrate excellent in resistance to phosphoric acid.
The other objects and the merits of the present invention will be clear to the persons skilled in the art from the following description.